Thermostatically heated limit switch



March 17, 1953 s. R. SHAFFER 2,632,083

THERMOSTATICALL HEATED LIMIT SWITCH Filed Dec. 1, 1950 2 SHEETSSHEET l Ff .5 H94 22 r 24 I8 9 30 I0 70 20 H46 52 66 /2 62 60 62 4 20 72 74 24 Inventor L J J .SIephen/ZS/raffer By um m Mafch 17, 1953 s sHAFFER 2,632,08 3

THERMOSTATICALLY HEATED LIMIT SWITCH- Filed Dec. 1, 1950 F 9- 2 @34 g g 2 SHEETSSHEET 2 Inventor Stephen R Shaffer Patented Mar. 17, 1953 THERMOSTATICALLY HEATED LIMIT SWITCH Stephen R. Shaffer, Fort Worth, Tex., assignor' to Luz E. Shaffer, Fort Worth, Tex.

Application December 1, 1950, Serial No. 198,533

7 Claims.

This invention comprises novel and useful improvements in switches, and more particularly pertains to improvements in heated switches.

It is well known that switches and relays on airplanes, and particularly on those planes which do not utilize heaters for the interior thereof, are subjected to wide variations in temperature. The cooler atmosphere at high altitudes causes condensation of the moisture on the switches and relays, which condensed moisture often causes electrical shorts which renders the switches inoperative. Further, the condensed moisture freezes, at low temperatures, and impairs movement of the various parts of the switch and switch operating mechanism. Accordingly, it is a primary object of this invention to maintain an electrical switch at a predetermined temperature to evaporate the moisture and prevent freezing thereof, so as to maintain the switch in an operative condition.

Another important object is to provide an electrically heated limit switch, of the type presently utilized on the bomb bay doors of airplanes, which heated limit switch may be interchanged with the conventional switch without requiring any modification in construction of the switch mounting or switch actuation.

Yet another object of this invention is to provide a heated limit switch in which the heating element is actuated only when the temperature falls below a predetermined minimum value.

An important feature of this invention resides in the provision of a switch housing having a top, bottom and side walls, with a pair of ribs on said bottom wall, a panel disposed on said ribs in spaced relation to the bottom wall and a heating coil disposed between the panel and the bottom wall, with the switch disposed on the upper face of the panel and secured to the ribs and a switch actuator extending through the side wall and engageable with the switch.

Another feature of this invention resides in the provision of a thermostat carried by the housing for controlling the energization of the heating coil.

These, together with various ancillary objects and features are attained by this device, a preferred embodiment of which has been illustrated in the accompanying drawings wherein:

Figure 1 is a perspective elevational view of the switch unit;

Figure 2 is an exploded assembly view of the switch unit;

Figure 3 is a transverse sectional view taken on the plane 33 of Figure l Figure 4 is a diagrammatic showing of the electrical circuit in the switch unit;

Figure 5 is a longitudinal sectional view of the switch unit, taken on the plane 55 of Figure 1, and

Figure 6 is a to plan view of the switch unit with a portion of the top broken away.

Reference is now made more specifically to the accompanying drawings wherein the switch unit is denoted generally by the numeral Ill.

The switch mechanism, and actuator therefore are conventional and form no part of this invention, that portion of the switch unit being presently manufactured under the trade name E. S. 4 Limit Switch.

The switch unit I0 includes a housing havinga bottom wall I2, side and end walls l4 and I6 respectively, and a removable top wall IS. A transverse partition 20 is disposed between the side walls I4 and is secured to the bottom wall I 2, which partition divides the housing into a first and a second chamber 22 and 24 respectively. Each of the corners of the housing are provided with enlarged reinforcing bosses 26 which are axially bored as at 28 for the reception of fasteners. The junctures of the partition 20 and each of the side walls are also reinforced by bosses such as 30, which have bores 32 therein. It is intended that the first chamber 22 be of the same dimensions as that of the housing of the E. S. 4 Limit Switch, so that the same or similar fastening bolts which are customarily disposed through the bosses in the opposed corners of that type E. S. 4 Limit Switch, may be disposed through the bosses 26 and 30 in the opposed corners of the first chamber to fasten the switch unit I0 to the conventional limit switch mounting (not shown). Fastening screws 34, which are provided with locking washers 36, are utilized to secure the cover l8 to the bosseson the housing, other than those through which the switch fastening bolts extend.

An enlarged centrally apertured boss 38 is formed on one of the end walls [6 and is provided with a bearing sleeve 4|] through which the switch actuating rod 42 extends, the inner end of the sleeve 40 being secured to a bearing plate 44 which is secured to one of the side walls l4 and has a bore therein through which the rod- 42 extends. A spring 46 is disposed between the inner end of the rod and the partition 20 to yieldingly bias the rodinto its inoperative position.

An actuating finger 48 is pivotally mounted by a pin 50 to a boss 52 carried by the bottom wall (see Figure 5), for movement parallel to the bottom wall, the finger 48 having a roller 53 journaled on the stub shaft 54 (see Figure 2) which roller is adapted to be engaged by a cam portion on the rod, the roller being moved into and out of the recess 56 in the sleeve 40 as the rod 42 is reciprocated.

A switch 58, of conventional construction, is secured by fasteners 60 to a pair of transverse ribs 62 carried by the bottom wall, the switch aceaoss 3 having a movable button 63 which is engaged by the finger 48, whereby the switch is actuated in response to movement of the finger 43 caused by reciprocation of the rod 42. As is best shown in Figure 5, the switch 58, the finger 48, and rod 42 are spaced from the bottom wall.

In order to electrically heat the switch unit It], there is provided a panel 64 which is supported by the ribs 62 in spaced relation to the bottom wall [2, and which underlies the switch 58, finger 48 and rod 42, the panel being of any suitable wear resistant material. It is to be noted that the panel is retained in position by the switch 58, and the fasteners which secure the latter to the ribs 62. A resistance heating coil 66 is disposed between the panel and the bottom wall of the housing, and is disposed about the ribs 62. A thermo-responsive switch 68 is attached to one leg of an L-shaped bracket, the other leg 72 of which is secured to the partition 20 by fasteners 14 whereby the thermo-responsive switch is supported in the second chamber 24. The conductors 16 and it which are connected to the heating coil, enter the housing through the same externally threaded sleeve 80 through which the switch conductors 82 and 84 extend.

The conductor '68 extends through an aperture in the partition and is connected to the thermoswitch 68, the conductor 26 leading from the switch also extending through the partition. Both the conductors l6 and 35 extend through apertures 88 in the panel 0 and are connected to the heating coil 66.

A suitable gasket 90 is interposed between the cover and the side walls of the housing for obvious reasons.

It is to be noted that the panel 64 is recessed at the corners thereof as at 92 for the reception of the reinforcing bosses 2B and 30, one of the corners being notched as at 94 to accommodate the bearing plate 44. Since the sleeve 45! encases that portion of the rod 42 between the plate 44 and the adjacent end wall I6, it will be appreciated that it is not necessary to extend the panel between the plate 44 and the adjacent end wall, to protect the heating coil from wear caused by the relative moving parts of the switch and switch actuator mechanism.

Having described the invention, what is claimed as new is:

1. A switch unit comprising a housing having a top, bottom and side walls, means disposed in said housing and attached to said bottom wall for supporting a switch in spaced relation thereto, an actuator reciprocably extending through one of said side walls and engageable with said switch to selectively actuate the same, a heating coil disposed between said bottom wall and said switch and switch actuator, and a thermostat carried by said housing for selectively energizing said heating coil, and a panel underlying said switch and switch actuator and overlying said heating coil.

2. A switch housing unit comprising a casing having a top, bottom and side walls, a pair of spaced ribs on said bottom wall, a panel disposed on said ribs in spaced relation to said bottom wall, a heating coil disposed between said panel and said bottom wall, and thermo-responsive means carried by said casing for controlling the actuation of said coil.

3. A switch housing for a heated switch unit comprising a casing having a top, bottom and side walls, a pair of spaced ribs on said bottom wall, a panel disposed on said ribs in spaced relation to said bottom wall, said panel being adapted to support a switch, a heating coil disposed between said panel and said bottom wall, and thermo-responsive means carried by said casing for controlling the actuation of said coil, a horizontally pivotally mounted actuator finger disposed in said housing above said panel and engaging said switch, and a reciprocably disposed actuator rod in said housing above said panel operatively engaging said finger.

4. A switch housing unit comprising a casing having a top, bottom and side walls, a pair of laterally spaced ribs carried by said bottom wall, an actuator reciprocably extending through one of said side walls, a bearing plate mounted on the adjacent side wall and slidably receiving said actuator, a panel disposed on said ribs and overlying said bottom wall in spaced relation thereto, said panel adapted to carry said switch, means fastening said panel to said ribs, said panel underlying said actuator and having a notch therein for the reception of said bearing plate, an actuating finger disposed above said panel in operative engagement with said actuator and said switch, a heating coil disposed below said panel, and thermo-responsive means for actuating said coil.

5. In a switch unit having a switch, a pivot-ally mounted actuator finger engaging said switch and a reciprocably disposed-actuator rod operatively engaging said finger, a housing comprising a casing having a top, bottom and side walls, a pair of spaced ribs on said bottom wall, a panel disposed on said ribs in spaced relation to said bottom wall, a heating coil disposed between said panel and said bottom wall, a partition dividing said casing into a plurality of compartments, a thermo-responsive means disposed in a compartment separated from the compartment housing the heating coil for controlling the actuation of said coil.

6. A housing for containing a switch comprising a top, bottom and side walls, ribs on said bottom, a panel mounted on said ribs in spaced relation to said bottom, said panel being adapted to support said switch, a heating coil disposed in the space between said bottom and said panel, and means responsive to a predetermined minimum temperature for energizing said heating coil.

7. A housing for enclosing a switch comprising a top, bottom and side walls, a switch carrying panel supported in said housing intermediate said top and bottom, a heating coil mounted between said panel and said bottom, a transverse partition in said housing, a temperature responsive switch mounted on said partition for controlling operation of said heating coil.

STEPHEN R. SHAFFER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,075,910 Robinson Apr. 6, 1937 2,223,234 Stemme Nov. 26, 1940 2,231,532 Grooms Feb. 11, 1941 2,274,285 Walker Feb. 24, 1942 2,512,220 Aske June 20, 1950 

